Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 171718
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1120 AM MDT WED AUG 17 2016

.SHORT TERM...Today Through Friday Night

The current ridging pattern remains this morning, with mountain
showers and thunderstorms developing. Warming temperatures also
expected to continue across the area today. Showers will see the
potential for small hail and gusty wind, with the western mountains
appearing most favorable for afternoon development. Showers will
continue through the evening pattern as the ridge breaks down.

A significant shift in the weather pattern will then begin late
tonight as a cold front sweeps through the state. Much cooler
daytime temperatures are anticipated across the area, and the shift
to a west-southwest flow will bring additional moisture across
central and western Wyoming. More widespread shower activity will be
possible, again containing some storm activity with hail and gusty
wind.

A second push of colder air will arrive across the area Friday
morning, resulting in even cooler temperatures, and another round of
showers and thunderstorms. Snow levels will potentially decrease
enough to permit some snowfall over the north-central mountains,
though accumulation should be generally light and result in little
to no impact for much of the state.

.LONG TERM...Saturday Through Wednesday

In wake of the storm system Friday, lingering valley rain/mid-high
mountain snow showers could occur east of the Divide Saturday.
However the models are trending drier over the last few runs.
Temperatures Saturday will remain well below average east of the
Divide where high temps are expected to be around 15 degrees below
average, while west of the Divide will be seasonal to only slightly
below average.

Sunday through Tuesday will see a warming trend and looks mainly dry
for now as the monsoonal moisture remains south of the area, and the
main storm track remains in Canada. This could change by Tuesday
night and Wednesday as models are showing the potential for a
shortwave trough and associated cold front diving southeast out of
Canada into the Northern Rockies.

&&

.AVIATION.../18Z ISSUANCE/

An weak upper level disturbance leading out from an approaching
upper level trough will arrive across West and Central Wyoming later
today. This system will bring isolated showers into the west this
morning and early afternoon, becoming more widely scattered with
thunderstorms later this afternoon. East of the Divide, showers and
storms will be more isolated. The main hazard will be gusty outflow
winds 30-45kts, with thunderstorm outflow winds likely dominating
the wind field in the late afternoon and early evening. Overnight
and through the Thursday morning hours, a cold front will push south
to vcnty the Montana/Wyoming border by around 06z Thursday and on to
vcnty KRIW-KBYG line by 12z Thursday, accompanied by a strong
northerly wind shift. Ceilings near FL150 and isolated showers will
linger 6z-12z Thursday across most of the area. Showers and
thunderstorms will arrive early Thursday morning, developing from
north to south across WY with a few strong storms expected early in
the Big Horn Basin then later in the afternoon across portions of
central/northern WY as the main disturbance passes by. Some of the
stronger storms will contain small hail and be able to produce
strong wind gusts greater than 45 mph.

&&

.FIRE WEATHER...

Warm conditions will persist today, with mountains showers and
thunderstorms possible this afternoon. Gusty and erratic wind may
accompany any storm activity. Significant changes in the weather
pattern are expected Thursday and Friday as much colder air moves
over the state. Below normal temperatures are anticipated, with
potentially widespread shower and thunderstorm activity during the
afternoons. Hail and gusty wind may remain threats with this system.

&&

.RIW Watches/Warnings/Advisories...None.

&&

$$

SHORT TERM...Branham
LONG TERM...WM
AVIATION...Braun
FIRE WEATHER...Branham



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